Shale inhibitor, also known as anti-collapse agent, is mainly used to prepare the inhibitory type of drilling fluid. When drilling into the mud shale formation, inhibit its hydration expansion and keep the well wall stable.
The commonly used shale inhibitors are:
Asphalt-type shale inhibitors
Before drilling in shale, supplying the drilling fluid with natural asphalt powder, when drilling in shale formation, if the softening point of asphalt and match the formation temperature, positive pressure differential action within the wellbore, asphalt can produce plastic flow, squeeze into shale pore and fracture , seal the crack and improve the bonding force of crack,to form inner mud cake and outer mud cake at the wellbore.There is a dense protective film between the outer mud cake and the formation, which makes it difficult to be washed, so as to prevent water from entering the formation and play the role of stabilizing the borehole wall.
Asphalt is the residue of crude oil refining. After certain processing of asphalt, it can be made into asphalt shale inhibitors for drilling fluid, including oxidized asphalt, sulphonated asphalt and KAHM which commonly known as high modified asphalt powder.
2. Potassium salt and humic acids
Its products include potassium humic acid (KHm), nitrocellulose potassium humic acid (MHP), sulphnated potassium humic acid, potassium silicone humic acid, potassium aluminum humic acid, aluminum humic acid and aluminum silicon humic acid, etc.
3. Cationic mud shale inhibitors
Cationic shale inhibitor (also known as clay stabilizer), the current field application is epoxy-propyl trimethyl ammonium chloride, commonly known as small cation.
Small cation inhibition debris dispersion effect is better than KCl, The advantage lies in that the cuttings surface adsorbed with small cation has certain hydrophobicity, which is not easy to adhere to the surface of drill bit, drill collar and drill pipe.
Small cations have a certain bactericidal effect, which can effectively prevent the biodegradation of some treatment agents;
Small cations do not affect the mineralization of drilling fluid obviously, and have the advantages of reducing the electrochemical corrosion of drilling tools downhole.
4. Amphoteric ion inhibitors
The polymer molecule has enhanced adsorption capacity on drilling cuttings, and can neutralize part of the negative charge of drilling cuttings, so it has a strong ability to inhibit drilling cuttings dispersion.
